X-ray tube



May 28, 1929. c, T, ULREY ET AL X-RAY TUBE Filed April 30, 1926 PatentedMay 2.8, 1929.

UNITED AS'fl`AfI'l5S PATENT OFFICE.

CLAYTON TBIDLE ULREY, OF EAST ORANGE, AND LOUIS F. EHRKE, F NEWARK.

NEW JERSEY, ASSIGNOBS TO WESTINGHOUSE LAMP COMANY, A. CORPORATION OFIENNSYLVANIA.

X-RAY TUBE.

Application filed Apl 80, 1926.1 Serial No. 105,640.

This invention relates to X-ray tubes and i more particularly to suchtubes adapted for general radiographic purposes.

The invention comprises certain improvements in the form of X-ray tubeillustrated and described iii the application of Clayton T. Ulrey,Serial No. 38,395, filed J une 20, 192.5.

The construction of the X-ray tube as dis-` closed by the aforementionedapplication for patent, comprises a cylindrical envelope having areentrant tube of high heat-resistant glass sealed at one end of theenvelope and extending to near the other end thereof. This tubesurrounds the anode stem and is also adapted to support the cathode. Theinner end of the reentrant tube extends beyond the face of the anode andis enclosed by a metal cup which is adapted to lscreen out undesirableX-radiation. The metal cup is of such size that it extends to each sideof the face yof the anode. In addition to supporting the metal cup, thereentrant tube also supports an insulating focusing device within whichthe thermionic cathode is supported.

In a tube of suoli design, if the voltage is high, electrical stresseswill be set up in that portion of the reentrant tube disposed within themetal cup and adjacent the face of the anode, due to the electrostaticpull between the positively charged anode and the negatively chargedmetal cup.

In order to adapt a tube of the foregoing design for generalradiographie purposes, it has been found desirable to modify somewhat,the internal structure of the tube, particularly at that portion of thetube where electrical stresses are set up.

' According to the present invention this has been accomplished bysupporting the metallic cup together with the focusing device andhot-cathode upon the inner sides of the glass envelope and shorteningthe reentrant tube housing to such an extent that it is not subjected todetrimental electrical stresses.

Referring to the drawings for a better understanding of the invention,

Fig. 1 is a longitudinal View partly in crosssection, of an X-ray tubeembodying the invention. y

Fig. 2 is an enlarged View of the metal cup,

illustrating the manner in which it is sup-- Fig. 3 is a view of themetal cup looking in the direction of the arrows in Fig. 2.

. An embodiment of the invention may comprise a glass envelope 4 ofcylindrical form having a reentrant tube 5.at one end, and aliemispherical glass enclosure 6 at its. other end. To the reentranttube 5 is sealed a support coupling 7, preferably of copper, having athin annular flange 8 towhich the reentrant tube 5 is hermeticallysealed. The coupling has atlireaded recess 9 in which is screwed acopper or other metallic rodl 11 which supports a radiator 12. Anotherthreaded opening 13 in the coupling, oppostely disposed with respect tothe recess 9, engages the threaded end 14 of the anode `15.

A target 16 of thorium or other good rayradiating material, is mountedin the rounded face 17 of the anode. The target may be formed as a cone17 so as to provide a larger surface upon which the electrons impingeand at the same time provide for a sharp focus or concentrated beam ofX-rays. A spring sleeve 18 threadedly secured to the anode 14frictionally engages the inner surface of a reentrant tube 19, to assistin supporting and maintaining the anode in proper position with respectto the cathode and other elements subsequently to be described.

The reentrant tube 19 is sealed or fused at 21 to the envelope 4 and isso spaced from the anode shank, that no detrimental ionization occurswithin such space. The tube 19 extends within the envelope to a pointbeyond the juncture of the anode 15 and the spring sleeve 18.

Disposed around the end of the anode is an X-iay screen 22 consisting ofnickel-iron. The X-ray screen comprises a cylinder 23, serving to screenout undesirable X-rays, a cap 24, having an opening 25 therein for theexit of the desirable X-rays, 4and a spring sleeve 26, slit at 27 (Fig.3) so as to forni four resilient tongues 28. The spring sleeve is ofsuoli character with respect to the inner target and end of the anode.If'desired, the v glass may be heated and pressed inwardly to engage anopening 28 inthe spring sleeve to Y of leading-in conductors 33, havingportions' 3l thereof capable of forming an hermetic seal with the glassenvelope. The cathode is so designed that it has an opening forpermitting the X-rays produced by electronic bombardment of the target16 to emerge from the tube via the passageways 31, 35 and 25 and theglass enclosure 6.

The X-ray screen, focusing device and cathode are assembled outside ofthe tube et in the following manner. vThe friction sleeve 26 may firstbe secured by the screws 3() to the cylinder 23, after which theinsulating focusing device 29 may be inserted in the end of thecylinder, annular shoulders 36 being provided for this purpose. vThehelical cathode 32 with the lead-wlres 33 secured thereto may y then bepositioned within the focusing device, with the ends 37 of the leadsinserted in openings 38 within the focusing member 29. A

Vmica. disk 39 having openings 41 through which the leads 33 arethreaded and a central opening 42 for the X-rays may then be placedwithin the focusing member. The focusing member, cathode and mica diskmay then be secured in position by means of the metal cap 24E which hasopenings 43 through which the lead wires 33 are threaded and aA centralopening 25. The cap is secured 'to the cylinder 23 by means of screws30. The assembly thus completed is inserted within the glass tube 4through the end which is subsequently closed by the spherical glassclosure 6. Previously to closing this end of the tube the seal wires 3lare secured to the lead wires 33 and sealed in the glass tube 4. The endof the glass tube 4 is then closed.

The spacing of the cathode with respect to the anode should be such thatit is less than the mean free path of the electrons for the pressure ofthe gas within the envelope. For example, with a gaseous pressure ofneon of 9 microns at room temperature (25 C.) the mean free path of theelectrons is approximately 10 cm. It is preferable to employ a factor ofsafety so that the ionization current is negligible as compared with thepureelectron current, and therefore, the spacing of the electrodesshould not be greater than 1/10 of the mean free path of the electrons.

A tube constructed in accordance with the' Y or against the outersurface of the envelop across the electrodes and with a current of 5milliamperes flowing between the electrodes. Even though there ispresenta considerable pressure of neon, no detrimental ionizationoccurs, however, ionization is present since it may readily be measuredby means of an ionization gage. Ve prefer to employ neon because oftherelatively small quantity of ionization therein and furthermore, becauseit is not so readily absorbed by the materials composing the tube. Theneon should be free of all other active gaseous constituents, but maycontain inert gases such iis-helium. In addition the glass partsas Wellas the metallic pin-ts of the tube, should be thoroughly freed o gas.

Although we have illustrated the metallic screen as disposed within theenvelope, the same results can be secured by providing upon e a layer ofmetal, such as lead, or any suita ld material which Will effectivelyabsorb X-rays. Furthermore, the screen may be combined with the casingmember which is usually employed with tubes of this Modifications of ourinvention may dccur to those skilled in the modification as come withinthe spirit and scope of the invention as defined by the appended claimsare contemplated by us.

What is claimed is:

1. An X-ray tube comprising an envelope containing an inert gas at asubstantial gas pressure, a reentrant insulating tube extending withinsaid envelope, an anode within said reentrant tube and extending beyondthe end thereof, an X-ray screen disposed around the end of said anodeand spaced from and free from the end of said reentrant tube and afocusing device and thermionic cathode supported by said X-ray screen.

2. In an X-ray tube having an envelope housing an anode and anincandescable cathode, au X-ray screen surrounding the end of lsaidanode, and resilient means for supporting said screen from the interiorwall of said envelope.

3. An X-ray tube comprising an envelope containing neon at about ninemicrons pressure, a reentrant tube of insulating material, an anodesupported by said reentranttube and closely spaced therefrom, a cathodeclosely spaced from the face of said anode, an insulating focusingdevice surrounding said cathode, and an X-ray screen surrounding theface of said ano de and supported by the inner wall of said envelope,said screen being out of -contact with said reentrant tu art, however,suchY a metallic X-ray screen disposed about the end of the anode out ofelectrical connection with said insulating sleeve.

5. An X-ray tube comprising an enclosing envelope, an anode and acathode therein, said envelope containing an inert gas at a substantialpressure, an insulating sleeve surrounding said anode, a metallic screendisposed about said cathode and the end of said anode, and spaced inelectrically non-conduc- 10 tive relation to said insulating sleeve.

In testimony whereof, We have hereunto subscribed our names this 28thday of April CLAYTON TRIDLE ULREY. f LOUIS F. EHRKE.

